CD4 and neoplasm: In order to determine the relative contributions of impaired tumor infiltration and loss of foxp3 expression to the decreased intra-tumor accumulation of Tregs, we repeated the adoptive transfer experiments described in Figure 4 using highly purified (>99% CD4+GFP+, 93% foxp3+ (data not shown)), FACS-sorted donor Tregs from foxp3GFP mice, in an attempt to track Tregs that become foxp3-negative within the tumor.